Introducing an NMR apparatus comprising cooled probe components via a vacuum lock

ABSTRACT

An NMR apparatus includes a superconducting magnet assembly, a cryostat having a vacuum vessel, a refrigeration stage that can be operated at a temperature of &lt;100 K, and a magnet coil system that comprises a cold bore into which a room temperature access of the cryostat engages. The NMR apparatus also includes an NMR probe with probe components cooled to an operating temperature of &lt;100 K. The probe components are arranged between the cold bore and the room temperature access into the cold bore, radially inside the cold bore but outside the room temperature access. The vacuum vessel includes an opening that can be closed by a lock valve. A lock chamber is directly connected to the opening, such that the cooled probe components can be installed and/or removed through the opening and lock valve without breaking the vacuum in the vacuum vessel of the cryostat.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims foreign priority under 35 U.S.C. § 119(a)-(d) toGerman Application No. 10 2016 214 728.5 filed on Aug. 9, 2016, theentire contents of which are hereby incorporated into the presentapplication by reference

FIELD OF THE INVENTION

The present invention relates to a cryogenic system for cooling asuperconducting magnet coil system and for cooling components of anuclear magnetic resonance (NMR) probe, for example for use in magneticresonance spectroscopy or magnetic resonance imaging (MRI). Theapplicability of the invention is not restricted to this field.

BACKGROUND

The invention relates to an NMR apparatus comprising a superconductingmagnet assembly including a cryostat which has a vacuum vessel and arefrigeration stage that can be operated at an operating temperature of<100 K. The superconducting magnet assembly also includes asuperconducting magnet coil system that comprises a cold bore into whicha room temperature access of the cryostat engages. The NMR apparatusalso includes an NMR probe being provided during operation thatcomprises probe components cooled to an operating temperature of <100 K.The invention also relates to a method for installing and removing thecooled probe components in/from the vacuum vessel of a cryostat of asuperconducting magnet assembly of an NMR apparatus.

Superconducting magnet coil systems are operated in a cryostat in orderto keep the temperature below the transition temperature of thesuperconductor. Typically, the cryostat has a vacuum vessel, in whichone or more cryogenic vessels each containing a coolant, for exampleliquid helium or liquid nitrogen, are arranged. The superconductingmagnet coil system is installed in the coldest cryogenic vessel. Thisresults in the superconducting magnet coil system being cooled in ahighly temperature stable and uniform manner. For example, NMRspectrometers are typically cooled in such a bath. In these systems, thevessels have to be refilled with the coolants at regular intervalsbecause the heat input to the cryogenic vessels ensures that thecoolants evaporate continuously. Alternatively, the coolants can berecondensed by a cryocooler on the cryostat, or cooling may be achievedby thermally attaching the superconducting magnet coil system and/or oneor more radiation shields of the cryostat to a refrigeration stage of acryocooler.

In order to install an NMR probe, the vacuum vessel of the cryostat istypically provided with a room temperature access into the cold bore ofthe superconducting magnet coil system. Given that operating the NMRprobe at room temperature is detrimental to signal quality, probescomprising cooled components are used. Various designs of cryogenicprobes of this kind are known. Usually, cryogenic probes are attached tothe room temperature access of the cryostat so as to be removable, thecooled components in this case being arranged in a separate insulationvessel and being cooled by a cooling circuit. Cryogenic probes that arefixedly mounted at least in part in the insulation vacuum of thecryostat are, however, also known.

Various cryogenic systems for cooling a superconducting magnet coilsystem and for cooling components of an NMR probe are known, whichdiffer in particular with respect to the mechanical integration of themagnet assembly and probe into a functional unit and with respect to thecommon use of components of the cryogenic system for cooling the magnetcoil system and the probe.

Some U.S. Pre-Grant publications (US 2012/0242335 A1, US 2007/0107445A1, US 2005/0202976 A1, US 2006/0130493 A1 and US 2013/063148 A1)generally describe assemblies comprising a cryogenic probe that isattached to the room temperature access of the cryostat of the magnetassembly so as to be removable.

In US 2012/0242335 A1 the cryogenic probe is cooled by means of acooling circuit which is thermally connected to a refrigerationreservoir of the cryostat of the magnet assembly, for example to aliquid nitrogen vessel.

In US 2007/0107445 A1, US 2005/0202976 A1, US 2006/0130493 A1 and US2013/063148 A1, the cryogenic probe and parts of the cryostat of themagnet assembly are cooled by means of a common cryocooler.

These assemblies are disadvantageous in that significant expense for thecooling circuit of the probe is required. Additionally, cooling capacitylosses result from the complexity of the instruments of the coolingcircuit. Furthermore, the cooled probe components have to be arranged ina separate insulation vacuum, which is detrimental to the compactness ofthe superconducting magnet coil system as a result of the increasedamount of space required by the cryogenic probe in the room temperatureaccess of the cryostat of the magnet assembly.

An assembly according to US 2012/0319690 A1 comprises a cryogenic probethat is installed in the vacuum vessel of the cryostat of thesuperconducting magnet assembly. This assembly is disadvantageous,however, in that the magnet assembly and cryogenic probe are no longermechanically modular. In order to replace the cryogenic probe, forexample when there is a fault or in order to carry out NMR measurementsthat place different requirements on the functional scope of thecryogenic probe, the cryostat vacuum has to be broken. Changing theprobe therefore requires that the superconducting magnet coil system bedischarged and the magnet assembly be warmed-up.

SUMMARY

An object of the present invention is to improve an NMR apparatus of thetype described at the outset comprising a superconducting magnet coilsystem in a cryostat. The NMR apparatus comprises a cryogenic probe, thecooled components of which are arranged inside the vacuum vessel of thecryostat during operation, such that the cooled probe components can bemoved into and out of the vacuum vessel without breaking the insulationvacuum in the vacuum vessel of the cryostat.

This object is achieved, according to one formulation of the invention,using cooled probe components that are arranged, at least in part, in aregion between the cold bore in the superconducting magnet coil systemand the room temperature access of the cryostat into the cold bore. Thecooled components are arranged radially inside the cold bore but outsidethe room temperature access of the cryostat. The vacuum vessel of thecryostat comprises an opening that can be closed with a lock valve, anda lock chamber which is directly connected to the opening or a devicefor attaching a lock chamber to the opening such that the lock chamberand opening are directly connected. The opening and the lock valve areof such a size and are arranged such that the cooled probe componentscan be installed and/or removed through the opening and lock valve.

The present invention thus proposes an NMR apparatus which makes itpossible to install/remove the cooled components of a cryogenic probeinto/from the vacuum vessel of the cryostat of a superconducting magnetassembly through a lock mechanism under a vacuum. Therefore, the magnetassembly does not have to be warmed up for this process and may remainin the charged state.

This assembly combines the advantages of a cryogenic probe that isarranged at least in part inside the vacuum vessel of the cryostat,namely that the structure is simple and space-saving without a separateinsulation vessel for the cooled probe components, and the advantages ofa cryogenic probe that is arranged inside the room temperature access ofthe cryostat, in particular that it is easy to install and remove thecryogenic probe if there is a fault or when different types of cryogenicprobes are being used for different NMR applications. Additionalfunctional units of the probe, such as an NMR sample rotor, may beplaced inside the room temperature access.

Some examples of the invention include a high frequency (HF) coilarranged in a region between the cold bore of the superconducting magnetcoil system and the room temperature access of the cryostat into thecold bore. The space-saving installation of cooled HF coils in thevacuum vessel of the cryostat without a separate insulation vessel isparticularly advantageous for the compact structure of thesuperconducting magnet coil system, since the HF coils are arrangeddirectly around the NMR sample within the working space of the magnetassembly.

In other examples, the NMR apparatus may include a mechanicallyreleasable thermal contact between the cooled probe components and arefrigeration stage of the cryostat. When cooling is carried out viathermal attachment to a refrigeration stage of the cryostat, a separatecooling device is not required for the cryogenic probe, and this is aparticularly cost-effective and thermally efficient solution.

Additional examples include the cryostat comprising a refrigerationstage with a nitrogen vessel. The cooled probe components are coupledthrough a releasable thermal contact to the refrigeration stage of thecryostat comprising the nitrogen vessel. These further examples utilizethe high cooling capacity brought about by the evaporation of liquidnitrogen and the thermal stability of the liquid nitrogen bath, and havebeen found to be a particularly cost-effective solution.

Further examples of the NMR apparatus are characterized in that thecryostat comprises a refrigeration stage with a radiation shield that iscooled by a single-stage cryocooler. The cooled probe components arecoupled through a releasable thermal contact to the refrigeration stageof the cryostat that comprises the radiation shield cooled by asingle-stage cryocooler. An advantage of a cryostat of a superconductingmagnet assembly comprising a radiation shield that is cooled in thismanner, as an alternative to a nitrogen vessel, is that the operatingtemperature of the radiation shield is lower than that of a vesselcooled by the evaporation of nitrogen. As a result, the cooled probecomponents can also be operated at a lower temperature. Furthermore, itis no longer necessary to periodically supply nitrogen.

Further, alternative examples of the NMR apparatus are characterized inthat the cryostat comprises a refrigeration stage with a radiationshield that is cooled by the first stage of a two-stage cryocooler. Thecooled probe components are coupled through a releasable thermal contactto the refrigeration stage of the cryostat that comprises the radiationshield cooled by the first stage of a two-stage cryocooler. An advantageof a cryostat of a superconducting magnet assembly comprising aradiation shield that is cooled in this manner, as an alternative to aradiation shield that is cooled by a single-stage cryocooler, is that asuperconducting magnet coil system, in particular having low-temperaturesuperconductors, can be cooled by thermal attachment to the second(colder) stage of the cryocooler. Additionally, helium gas from a heliumvessel of the cryostat can be condensed on the second stage of thecryocooler.

Further alternative examples of the NMR apparatus are characterized inthat the cryostat comprises a refrigeration stage with a superconductingmagnet coil system that is cooled by a single-stage cryocooler. Thecooled probe components are coupled through a releasable thermal contactto the refrigeration stage of the cryostat that comprises thesuperconducting magnet coil system cooled by a single-stage cryocooler.These alternative examples are advantageous in particular forcryogen-free superconducting magnet assemblies that include asuperconducting magnet coil system with high-temperaturesuperconductors. A magnet coil system of this kind can be cooled totemperatures which are sufficiently low for efficient operation bythermal attachment to a single-stage cryocooler.

Another example of the NMR apparatus is characterized in that themechanically releasable thermal contact comprises thermal contactelements which are formed on either side of the mechanically releasablethermal contact as a cone and an interlocking mating cone. The cone andmating cone may be produced from a heat-conductive material having aheat conductivity at the operating temperature of the assembly ofgreater than 20 W/(K*m), in particular copper. The cone and mating conemay also be coated with a noble metal, in particular gold. The cone andmating cone may be pressed against one another in the operating state bya spring element with a force of at least 20 N. This results in optimumheat transfer between the cooled probe components and a refrigerationstage of the cryostat.

In some examples of the NMR apparatus, the cooled probe components maybe cooled from outside the cryostat using an external cooling circuit.This significantly simplifies the mechanics, because the cooled probecomponents do not need to be thermally attached to a refrigeration stageof the cryostat. Furthermore, the thermal equilibrium of therefrigeration stages of the cryostat, in particular the refrigerationstage cooling the superconducting magnet coil system, is not disruptedas a result of thermal loads by the cooled probe components. Therequired cooling capacity can be adapted to the heat input of the probe,independently of the cooling of the cryostat. This example isparticularly advantageous when the probe has a high thermal output.

The cooled probe components of the NMR apparatus according may includenormally conducting and/or superconducting components. Normallyconducting components are cost-effective and have lower requirements interms of cooling. In contrast, superconducting components produce bettersignal quality.

In one example, a mechanically releasable thermal contact is providedbetween the cooled probe components and a refrigeration stage of thecryostat. The cooled probe components can be cooled from outside thecryostat using an external cooling circuit, with the probe-side thermalcontact element being colder than the thermal contact element of therefrigeration stage of the cryostat in the operating state of theassembly. This assembly makes it possible to utilize the coolingcapacity of a cooling circuit comprising a high-performance cryocoolerarranged outside the cryostat not only to cool the probe components, butalso to absorb heat from a refrigeration stage of the cryostat, forexample, from a radiation shield arranged around a cryogenic vessel.This can, for example, reduce the evaporation rate of cryogenic liquidsfrom a cryogenic vessel of the cryostat assembly.

In other examples of the NMR apparatus, the NMR probe is designed suchthat, in the installed state, part of the NMR probe can close the openlock valve in the opening of the vacuum vessel in an air-tight manner.This enables the lock chamber to be detached in the operating state. Adetachable lock chamber enables improved protection against loss ofvacuum and access to the warm end of the installed NMR probe forcontacting electrical connections or cooling lines.

In further examples, a lift mechanism is provided in the lock chamberfor raising and lowering the cooled probe components out of/into thevacuum vessel. This allows the probe to be raised and/or lowered in acontrolled and precise manner.

Examples of the NMR apparatus may include low-temperaturesuperconductors (LTS) or high-temperature superconductors (HTS). Inorder to cool magnet coil systems comprising LTS to the required lowoperating temperatures of a few Kelvin, cryostat assemblies may includea plurality of cascade-connected refrigeration stages, which offerparticularly diverse options for thermally attaching cooled probecomponents. Magnet coil systems comprising HTS can be operated atsimilar temperatures to cooled probe components, which renders thermaland mechanical integration of these two components of an NMR apparatusparticularly advantageous.

In another example, the magnet assembly may include a shim system, suchas an active shim system comprising shim coils or a passive shim systemcomprising one or more ferromagnetic field-shaping elements, inside thecryostat in order to homogenize the magnetic field. The shim system maybe arranged between the cold bore of the superconducting magnet coilsystem and the cooled probe components. The shim system may also bethermally attached to a refrigeration stage of the cryostat or to anexternal cooling circuit. Arranging the shim system inside the cold boreof the superconducting magnet coil system (i.e., near the NMR sample)produces a highly efficient shim system, but the efficiency of the HFcoils is not impaired by the shim system being arranged radially outsidethe cooled probe components. Cooling the shim system preventsundesirably high thermal gradients between the superconducting magnetcoil system, shim system and cooled probe components.

A method for installing/removing cooled probe components in/from thevacuum vessel of a cryostat of a superconducting magnet assembly of anNMR apparatus according to the invention is also covered by the presentinvention and may be characterized by the following steps:

-   -   1. decoupling connection lines of the NMR probe to other parts        of the NMR apparatus;    -   2. attaching a lock chamber to the lock valve;    -   3. evacuating the lock chamber;    -   4. moving the probe components to be removed out of the vacuum        vessel of the cryostat and into the lock chamber;    -   5. closing the lock valve;    -   6. flooding and opening the lock chamber, and taking out the        probe components to be removed;    -   7. introducing the probe components to be installed into the        lock chamber, and closing and evacuating the lock chamber;    -   8. opening the lock valve;    -   9. moving the probe components to be installed out of the lock        chamber and into the vacuum vessel of the cryostat;    -   10. flooding and removing the lock chamber; and    -   11. coupling the connections of an external cooling circuit to        the NMR probe.

This method enables the cooled probe components to be interchangedwithout breaking the cryostat vacuum, and without warming up the magnetassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the drawings and is explained in greaterdetail with reference to the embodiments. In the drawings:

FIG. 1 is a schematic view of a first example embodiment of the NMRapparatus according to the invention in the operating state, when thelock chamber is detached.

FIG. 2 shows an example embodiment of the NMR apparatus having a lockchamber coupled thereto via a lock valve.

FIG. 3 is a schematic view of an example embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached, also showing a helium vessel, a radiation shield, and anitrogen vessel.

FIG. 4 is a schematic view of an example embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached, also showing a helium vessel, two radiation shields, and asingle-stage cryocooler.

FIG. 5 is a schematic view of an example embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached, also showing a two-stage cryocooler, a radiation shield,and a helium vessel.

FIG. 6 is a schematic view of an example embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached, also showing a two-stage cryocooler, a radiation shield,and a cryogen-free magnet.

FIG. 7 is a schematic view of an example embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached, also showing a single-stage cryocooler, a radiation shield,and a cryogen-free superconducting magnet coil system that is based onhigh-temperature superconductors.

FIG. 8 is a schematic view of an example embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached, also showing a helium vessel, two radiation shields, and asingle-stage cryocooler, and showing the cooled probe components coupledto the radiation shields via thermal contact elements.

FIG. 9 is a schematic view of the thermal contact elements of FIG. 8, inwhich the probe-side thermal contact elements are cooled by an externalcoolant stream circulating from a cryocooler of the NMR probe.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of a first embodiment of the NMR apparatusaccording to the invention in the operating state, when the lock chamberis detached.

FIG. 2 shows the same embodiment as FIG. 1, in which a lock chamber 112is coupled to the vacuum chamber 102 of the cryostat from below via alock valve 109 in order to introduce the NMR probe 11 into the cold bore101 of the cryostat.

FIG. 1 and FIG. 2 illustrate two states of the NMR apparatus accordingto the invention achieved during installation/removal of probecomponents in/from the vacuum vessel of the cryostat. In this case, FIG.1 corresponds to the state before decoupling connection lines of the NMRprobe 11 to other parts of the NMR apparatus, or after coupling theconnections of an external cooling circuit to the NMR probe 11. FIG. 2corresponds to the state between closing the lock valve 109 and floodingand opening the lock chamber 112, and taking out the removed probecomponents 9, 10. In the operating state (e.g., FIG. 1), the NMR probe11 is connected to other parts of the NMR apparatus via electrical andoptionally fluid lines (see, for example, FIG. 9). These lines aredecoupled from the NMR probe 11 in a first step of a method for removingthe NMR probe. This then makes it possible for the lock chamber 112 tobe attached in a vacuum-tight manner to the vacuum vessel 102 of thecryostat via the sealing rings 114. After the lock chamber 112 has beenevacuated by the pump-out valve 113, the lock valve 109 can be opened,and the NMR probe 11 is brought out of the operating position and intothe removal position by a mechanical guide, either by an internalstructure (e.g. electrically operated lift) or by a shaft guided throughthe lock chamber 112. In the removal position, the entire NMR probe 11is below the plane of the lock valve 109, and the lock valve 109 can beclosed, resulting in the state illustrated in FIG. 2. The NMR probe 11is warmed-up from the operating temperature of the magnet to close toroom temperature, preferably in the lock chamber 112. Otherwise iceand/or condensed water may accumulate on the NMR probe 11, which coulddamage the NMR probe 11. In addition, rapid changes in temperature alsolead to large internal mechanical stress, which can damage the NMR probe11.

Warming up the NMR probe 11 takes place primarily by heat radiation inthe evacuated state of the lock chamber 112. However, a small amount(e.g., 1 mbar) of helium gas can be transferred into the lock chamber inorder to thermally couple the NMR probe 11 to the lock chamber 112 byweak convective heat transfer. Alternatively, an electrical heatingstructure on the NMR probe 11 may heat up the NMR probe 11 in acontrolled and gentle manner. Once the NMR probe 11 has been heated toroom temperature, the lock chamber 112 is flooded. Then, the lockchamber 112 is detached together with the NMR probe 11 by releasing thevacuum-tight connection (e.g., sealing rings 114). The NMR probe 11 canthen be removed from the lock chamber 112, and a second NMR probe 11 maybe inserted into the lock chamber 112. Once the lock chamber 112 hasbeen evacuated, the lock valve 109 is opened, and the second NMR probe11 may be introduced into the superconducting magnet assembly 27 slowlyenough for the second NMR probe 11 to be cooled slowly but continuously(e.g., by radiation), such that the thermal shock when being coupled tothe refrigeration stages of the cryostat is minimized.

Once the second NMR probe 11 has been mechanically coupled to thesuperconducting magnet assembly 27 and the second NMR probe 11 has beensecured in the operating position, the connection of the second NMRprobe 11 to the vacuum vessel 102 of the cryostat is vacuum tight withrespect to the atmosphere, and the lock chamber 112 can be flooded usingthe pump-out valve 113 and removed.

Finally, the electrical and (optionally) fluid lines of the second NMRprobe 11 to the NMR apparatus are reconnected to the second NMR probe11. This concludes the method for removing a first NMR probe 11 andinstalling a second NMR probe 11.

FIGS. 3 to 8 show the shim system 104 in the cold bore 101 of thesuperconducting magnet coil system 111. This shim system 104 can includepassive elements (e.g., iron shims) which influence the field as aresult of their magnetic susceptibility, in that the geometricdistribution is used to correct field inhomogeneity. These passive shimsare attached to a mechanical support structure. In this respect, a metaltube, for example, may form part of a radiation shield 21 or 110, andcan be in thermal and mechanical contact therewith. The shim system 104can however also be constructed from active components. In this case,the shim system 104 comprises conductor loops through which currentpasses and which are typically made of a good electrical conductor, suchas copper or even superconductor material. In both cases, coupling to arefrigeration stage of the cryostat is advantageous or, in the case ofsuperconductors, typically required. In this case too, the shim system104 may be mounted on a support tube which is, for example, thermallyconnected to a radiation shield 21 or 110.

FIG. 3 shows an example of the superconducting magnet assembly 27comprising a helium vessel 105, radiation shield 110 and nitrogen vessel18. The nitrogen vessel 18 is thermally coupled to the NMR probe 11comprising the cooled probe components 9, 10. This enables the nitrogenvessel 18 to cool the cooled probe components 9, 10. The radiationshield 110 may be cooled by residual enthalpy of the cryogenic heliumgas flowing from the helium vessel 105, and is at an equilibriumtemperature that is between the temperature of the helium vessel 105 andthat of the nitrogen vessel 18.

FIG. 4 shows an embodiment comprising a single-stage cryocooler 301instead of a nitrogen vessel 18. The cryocooler 301 cools a furtherradiation shield 21 that surrounds the radiation shield 110. Theradiation shield 21 is in this case typically at a temperature ofbetween 30 and 90 Kelvin. As in the case described with respect to FIG.3, the radiation shield 110 may be cooled by residual enthalpy of thecryogenic helium gas flowing from the helium vessel 105, and is at anequilibrium temperature that is between the temperature of the heliumvessel 105 and the temperature of the further radiation shield 21. TheNMR probe 11 coupled to the refrigeration stage of the cryostat that iscooled by the single-stage cryocooler 301 results in the cooled probecomponents 9, 10 being cooled by the cryocooler 301. In this manner, thecooled probe components 9, 10 may be operated within a temperature rangeof between 30 and 90 Kelvin. Temperatures significantly above thistemperature range would likely result in performance losses in the NMRmeasurements. If, on the other hand, the cooled probe components 9, 10were to be coupled to the helium vessel 105 or the colder radiationshield 110 at a significantly lower temperature, the power dissipated inthe cooled probe components 9, 10 could no longer be conducted away bythe cryocooler 301. The power dissipated in the cooled probe components9, 10 may have to be cooled by the evaporation of liquid helium from thehelium vessel 105, which would lead to a significant increase in theamount of helium consumed. The example shown in FIG. 4 thereforecombines low helium consumption with good NMR performance.

FIG. 5 shows an embodiment comprising a two-stage cryocooler 309.Similar to the example described with respect to FIG. 4, the first stage307 of the cryocooler 309 is coupled to the radiation shield 21, whichis coupled to the cooled probe components 9, 10 via said radiationshield 21. This subsystem cooled by the first stage 307 of thecryocooler 309 operates in a similar way as the example described inFIG. 4 in terms of heat flow. In addition, however, the cryocooler 309has a second stage 308 which provides cooling capacity at a temperaturebelow the boiling point of helium. Through this cooling capacity, heliumevaporated in the helium vessel 105 is immediately recondensed in thehelium vessel 105, without leaving the helium vessel 105. A radiationshield 110 cooled by residual enthalpy of helium gas flowing from thehelium vessel 105, as shown in FIG. 4, is omitted in this example. Thisexample combines the good NMR performance of the embodiment according toFIG. 4 with a virtually unlimited helium hold time.

FIG. 6 shows a further example of the assembly from FIG. 5. The thermaldesign is identical, but the magnet 111 is no longer housed in a heliumvessel 105. The magnet 111 is thermally coupled to the second stage 308of the cryocooler 309 using solid structures (e.g. made of copper).Since, in this case, there is neither helium nor nitrogen in the system,this example is a cryogen-free embodiment. The use of a two-stagecryocooler 309 makes it possible to use cost-effective niobium-basedlow-temperature superconductors or MgB2 owing to the typically very lowbase temperature of the second stage 308, typically in the range ofsingle-digit Kelvin values.

FIG. 7 shows an example which is based on a single-stage cryocooler 301.The first (and only) stage 307 of the cryocooler 301 is coupled to theradiation shield 21. The first stage 307 is coupled to the cooled probecomponents 9, 10 via the radiation shield 21, and further coupled to acryogen-free superconducting magnet coil system 111. The operatingtemperatures that can typically be reached in single-stage cryocoolers(e.g., at a total thermal load from 5 to 20 Watts) are typically 40Kelvin or higher, which restricts the superconducting magnet assembly 27to superconducting magnet coil systems 111 based on high-temperaturesuperconductors.

FIG. 8 shows an example of a releasable thermal contact 106 between theNMR probe 11 comprising the cooled probe components 9, 10, and theradiation shields 21, 110 from the example shown in FIG. 4. The thermalconnection is brought about by a probe-side thermal contact element 302and by a refrigeration-stage-side thermal contact element 303, which aretypically formed as a gold-coated cone and mating cone. Each cone may besupported by a spring element 306 which ensures that there is therequired contact pressure on the mating cone. This force issignificantly strengthened by the specific geometry of the cone, sincethe axial force supplied by the spring element 306 results in a normalforce on the contact surface that is increased by up to an order ofmagnitude. The increased normal force ultimately provides for thethermal coupling between the cone and the mating cone. The cooled probecomponent 9 comprises, in this embodiment, an HF coil, which is coupledto the colder radiation shield 110. The cooled probe component 10, forexample an electronic amplifier component, is operated at the highertemperature of the warmer radiation shield 21.

FIG. 9 shows an example of the NMR apparatus in which refrigerationstages of the cryostat of a superconducting magnet assembly 27 andcooled probe components 9, 10 of an NMR probe 11 are cooled togetherusing an external cryocooler 2 of the NMR probe 11. In this case, acoolant stream conveyed by the compressor of this cryocooler 2 flows, insuccession, through a first counter flow heat exchanger, a heatexchanger on the first stage 3 of the cryocooler 2, a counter flow heatexchanger 8 and a heat exchanger on the second stage 4 of the cryocooler2 until the coolant has cooled down to a temperature of typically closeto 10 Kelvin. The coolant is then guided through a heat-insulated lineto the NMR probe 11 and is coupled here to the colder probe-side thermalcontact element 302 via a heat exchanger, and then flows back into theheat-insulated housing 1 of the cryocooler 2. After passing through thecounter flow heat exchanger 8, the coolant flows to the heat exchangeron the warmer probe-side contact element 302, and from there flows backinto the heat-insulated housing 1 and finally back to the compressor viathe first counter flow heat exchanger.

The cooled probe components 9, 10 are connected to the probe-sidethermal contact elements 302 in a heat-conducting manner, for examplethrough a heat-conducting mechanical structure 304.

The example shown in FIG. 9, which includes thermally attaching theprobe-side thermal contact element 302 to a cooling circuit cooled by anexternal cryocooler 2 of the NMR probe 11, is the reverse of the exampledescribed in FIG. 4 in terms of heat flow. In this example, thesuperconducting magnet assembly 27 is cooled alongside with the cooledprobe components 9, 10 by the cryocooler 2 of the NMR probe 11, whereasin FIG. 4 the cooled probe components 9, 10 of the NMR probe 11 arecooled alongside with the superconducting magnet assembly 27 by thecryocooler 301 of the cryostat of the superconducting magnet assembly27.

An assembly comprising a cryocooler 2 of the NMR probe 11 that has justone stage is also conceivable. In this case, the counter flow heatexchanger 8 and the second stage 4 of the cryocooler 2 may be omittedfrom the example described in FIG. 9. This results in highertemperatures on the cooled probe components 9, 10, which may lead toreduced NMR performance which may, however, be adequate in someapplications.

In another example, the cooled probe components 9, 10 may be cooled by acoolant stream from the external cryocooler 2, and the refrigerationstages of the cryostat may be cooled by a cryocooler 301 of the cryostator by the evaporation of cryogenic liquids. In this case, thermalcoupling between the refrigeration stages of the cryostat and the cooledprobe components 9, 10 can be dispensed with, and the thermal contactelements 302, 303 may be omitted.

LIST OF REFERENCE NUMERALS

-   1 heat-insulated housing-   2 cryocooler of the NMR probe-   3 first stage of the cryocooler 2-   4 second stage of the cryocooler 2-   8 counter flow exchanger-   9 cooled probe component-   10 cooled probe component-   11 NMR probe-   18 nitrogen vessel-   21 radiation shield-   27 superconducting magnet assembly-   101 cold bore of the superconducting magnet coil system-   102 vacuum vessel of the cryostat-   103 room temperature access-   104 shim system-   105 helium vessel-   106 releasable thermal contact-   107 thermal insulation-   108 opening in the vacuum vessel-   109 lock valve-   110 radiation shield-   111 superconducting magnet coil system-   112 lock chamber-   113 pump-out valve-   114 sealing ring-   301 single-stage cryocooler of the cryostat-   302 probe-side thermal contact element-   303 thermal contact element of the refrigeration stage of the    cryostat-   304 heat-conducting mechanical structure-   306 spring element-   307 first stage of the cryocooler-   308 second stage of the cryocooler-   309 two-stage cryocooler of the cryostat

What is claimed is:
 1. A Nuclear Magnetic Resonance (NMR) apparatuscomprising: a superconducting magnet assembly comprising: a cryostatwith a vacuum vessel and a refrigeration stage at an operatingtemperature of <100 K, wherein the vacuum vessel includes an openingoperable to be closed with a lock valve, and a lock chamber which isdirectly connected to the opening or a device for attaching the lockchamber to the opening such that the lock chamber and the opening aredirectly connected; and a superconducting magnet coil system with a coldbore into which a room temperature access of the cryostat engages; andan NMR probe including probe components cooled to an operatingtemperature of <100 K, wherein the cooled probe components are arranged,at least in part, in a region between the cold bore of thesuperconducting magnet coil system and the room temperature access ofthe cryostat into the cold bore, radially inside the cold bore andoutside the room temperature access of the cryostat, wherein the openingand the lock valve are sized and arranged such that the cooled probecomponents are installed and/or removed through the opening and the lockvalve.
 2. The NMR apparatus according to claim 1, wherein the cooledprobe components arranged in the region between the cold bore of thesuperconducting magnet coil system and the room temperature access ofthe cryostat into the cold bore include a high frequency (HF) coil. 3.The NMR apparatus according to claim 1, further comprising amechanically releasable thermal contact between the cooled probecomponents and the refrigeration stage of the cryostat.
 4. The NMRapparatus according to claim 3, wherein the refrigeration stagecomprises a nitrogen vessel, and wherein the cooled probe components arecoupled through the mechanically releasable thermal contact to thenitrogen vessel.
 5. The NMR apparatus according to claim 3, wherein therefrigeration stage comprises a radiation shield, which is cooled by asingle-stage cryocooler, and wherein the cooled probe components arecoupled through the mechanically releasable thermal contact to theradiation shield cooled by the single-stage cryocooler.
 6. The NMRapparatus according to claim 3, wherein the refrigeration stagecomprises a radiation shield which is cooled by a first stage of atwo-stage cryocooler, and wherein the cooled probe components arecoupled through the mechanically releasable thermal contact to theradiation shield cooled by the first stage of the two-stage cryocooler.7. The NMR apparatus according to claim 3, wherein the superconductingmagnet coil system is cooled by a single-stage cryocooler, and whereinthe cooled probe components are coupled through the mechanicallyreleasable thermal contact to the superconducting magnet coil systemcooled by the single-stage cryocooler.
 8. The NMR apparatus according toclaim 3, wherein the mechanically releasable thermal contact comprises afirst thermal contact element formed as a cone and a second thermalcontact element formed as an interlocking mating cone, the cone and theinterlocking mating cone being produced from a heat-conductive materialhaving a heat conductivity of greater than 20 W/(K*m) at the operatingtemperature, wherein the cone and the interlocking mating cone arecoated with a noble metal, and wherein the cone and the interlockingmating cone are pressed against one another by a spring element with aforce of at least 20 N.
 9. The NMR apparatus according to claim 8,wherein the heat-conductive material comprises copper, and wherein thenoble metal comprises gold.
 10. The NMR apparatus according to claim 1,wherein the cooled probe components are cooled from outside the cryostatwith an external cooling circuit.
 11. The NMR apparatus according toclaim 1, wherein the cooled probe components include normally conductingor superconducting components.
 12. The NMR apparatus according to claim3, wherein the mechanically releasable thermal contact comprises aprobe-side thermal contact element and a refrigeration-stage-sidethermal contact element, the probe-side thermal contact element beingcolder than the refrigeration-stage-side thermal contact element. 13.The NMR apparatus according to claim 1, wherein the NMR probe isdesigned such that, in an installed state, a part of the NMR probecloses the lock valve in the opening of the vacuum vessel in anair-tight manner, enabling the lock chamber to be detached.
 14. The NMRapparatus according to claim 1, wherein the superconducting magnet coilsystem comprises low temperature superconducting (LTS) elements or hightemperature superconducting (HTS) elements.
 15. The NMR apparatusaccording to claim 1, wherein the superconducting magnet assemblyincludes a shim system, and wherein the shim system includes an activeshim system comprising shim coils, or a passive shim system comprisingone or more ferromagnetic field-shaping elements, and wherein the shimsystem is arranged inside the cryostat in order to homogenize a magneticfield, and wherein the shim system is arranged between the cold bore ofthe superconducting magnet coil system and the cooled probe components,and wherein the shim system is thermally attached to the refrigerationstage of the cryostat or to an external cooling circuit.
 16. A methodfor installing and removing probe components in/from the vacuum vesselof the cryostat of the superconducting magnet assembly of the NMRapparatus according to claim 13, the method comprising: decouplingconnection lines of the NMR probe to other parts of the NMR apparatus;attaching the lock chamber to the lock valve; evacuating the lockchamber; moving probe components to be removed out of the vacuum vesselof the cryostat and into the lock chamber; closing the lock valve;flooding and opening the lock chamber, and taking out the probecomponents to be removed; introducing probe components to be installedinto the lock chamber, and closing and evacuating the lock chamber;opening the lock valve; moving the probe components to be installed outof the lock chamber and into the vacuum vessel of the cryostat; floodingand removing the lock chamber; and coupling connections of an externalcooling circuit to the NMR probe.